User manual

GMC-I Messtechnik GmbH 41
Measurements: V/Hz, , , Temp (°C/°F), , M
@UISO
, A/Hz
Automatic Recognition of Interference Voltage
during Insulation Resistance Measurement
If the instrument detects interference voltage of greater than
15 V AC or > 25 V DC during insulation testing (condition: U
interference
 U
ISO
, e.g. Riq < 100 k at 100 V, see Seite 62, footnote 1), Error
is briefly displayed at the LCD. The instrument is then
automatically switched to voltage measurement, and the currently
measured voltage value is displayed.
Note
A dead zone results in erroneous measurements for
automatic interference voltage detection during insulation
resistance measurement. The dead zone lies within a range
of 80% to 120% of the selected test voltage (in the case of
an interference voltage whose value is equal to that of mea-
suring voltage, the two voltages neutralize each other).
Manual switching to insulation resistance measurement is
disabled for as long as voltage is applied to the test terminals.
If interference voltage is no longer present, the M
@ISO
measure-
ment can be started by once again pressing the UISO ON / OFF key.
Attention!
!
If Error appears at the display, the cable (the device under
test) is most likely capacitively charged to a significant ex-
tent. Remedy: Short circuit the cable (the device under test).
Repeat the measurement.
Special case indication of low insulation resistances up to short circuit
First „Error“ is displayed, and then briefly „Short“, followed by the
current resistance measured value.
5.7.3 Ending the Measurement and Discharging
➭ Briefly press the U
ISO ON / OFF key.
After measurement has been completed, any remaining residual
voltage is displayed which may result from cable capacitance.
The instrument’s internal 1 M resistor causes rapid discharging.
However, contact to the device under test must be maintained.
The falling voltage value can be observed directly at the LCD.
Do not disconnect the device under test until the voltage value has
dropped to < 25 V!
Note
The instrument’s batteries are rapidly depleted during insula-
tion resistance measurement. Deactivate insulation resis-
tance measurement between measurements for this reason.
Use only alkaline manganese batteries in accordance with
IEC 6 LR61.
Note
Rotary selector switch position “V1 M  / M 
@UISO
” is avail-
able for the detection of interference voltage during insula-
tion resistance measurement.
Use switch position V , V or V in order to perform
precise voltage measurements.
+
–
0V !
Discharge
025.0
UISO
V
DC
AC
TRMS
ISO 500 V